Caught red-handed: Detection of latent fingerprints through release of fluorescein from a nanofiber mat

When a forensic agent dusts a surface with powder or exposes it to the vapors of an iodine chamber, mystery fans know what is going on: This is how latent fingerprints are made visible so that they can be compared to those of a suspect. Su Chen and a team at Nanjing University of Technology have now developed a new process for especially rapid and simple detection of fingerprints. As the Chinese researchers report in the journal Angewandte Chemie, all it takes is a special nanofiber mat that is pressed onto the suspect surface and briefly treated with hot air -- the fingerprints appear as red ridge patterns.

When we touch a surface, tiny traces of perspiration and oils stay behind, mirroring the ridge patterns on our fingertips. There are now a number of different methods to make these latent fingerprints visible. The new method is significantly faster than the classic technique of dusting with powder. Unlike spectroscopic methods, it does not require complex technical instruments, and problematic chemicals like ninydrin are not needed either. In addition, it is suitable for all types of surfaces: by lightly pressing the mat onto the surface, the researchers were able to reliably transfer fingerprints from a wide variety of materials, including steel, quartz, glass, plastic, marble, and wood.

The secret of their success is the special mat, a fleece made from nanofibers of thermoplastic polyurethane and fluorescein, a dye. The mat is made in a process called electrospinning. When the mat comes into contact with a fingerprint, components of the perspiration react with the polyurethane, causing cross-linking of the polymer chains. The hot air accelerates the reaction. In the cross-linked regions, the fluorescein cannot remain within the fibers so it comes out as a powdery solid. However, the dye only fluoresces when it is very finely dispersed in the nanofibers, not when it is in small solid clumps. This causes the color of the mat to change from straw yellow to red, making the fingerprint visible within 30 seconds in daylight. The method only works with nanofibers, because only they have enough surface area to produce a visible reaction.

The mat can identify more than mere fingerprints. The researchers were able to "print" an image of a small dragon onto the mat by using an ink-jet printer. Their ink was simply water, which can also cause the cross-linking reaction. The combination of ink-jet printing and the release of a chemical from a nanofiber mat could also be used to produce miniaturized systems such as sensors, microreactors, and diagnostic chips.

More information: Su Chen, et al., A Release-Induced Response for the Rapid Recognition of Latent Fingerprints and Formation of Inkjet-Printed Patterns, Angewandte Chemie International Edition 2011, 50, No. 16, 3706–3709, Permalink to the article: http://dx.doi.org/ … ie.201006537

Provided by Wiley (news : web)

Cements that self-repair cracks and store latent heat energy?

 Cement (and derivatives thereof) is one of the materials most commonly used in construction, given its good performance at low cost. Over recent years, one part of scientific and technological research is aimed at incorporating additional functions into these materials. Specifically, Doctor Idurre Kaltzakorta studied the possibility of adding capacities to the cement such as self-repair of cracks as well as storing latent heat energy.

Her PhD thesis, undertaken at Tecnalia's Construction Unit, was presented at the University of the Basque Country (UPV/EHU) and entitled: Synthesis of silica microcapsules encapsulating different organic compounds for addition in the cement paste.

As the title of her research suggests, Dr Kaltzakorta created silica (it is, for instance, the base of glass) microcapsules with organic material inside, the idea being to provide the cement with new functions. She opted for two types of organic materials, each corresponding to one of the two added features mentioned above. Thus, on the one hand, the microcapsules were filled with various epoxy resins (used in the manufacture of adhesives), to provide the cement with the capacity for the self-repair of cracks. On the other, phase change materials were encapsulated. These are materials which absorb or free a great quantity of heat on the phase of the material changing (from solid to liquid or liquid to gas and vice-versa), and enable the storage of latent heat energy in the cement material.

Sol-gel and emulsion

Ms Kaltzakorta studied the synthesis of the encapsulated material, opting for synthesising microcapsules by combining sol-gel chemistry with emulsion technology. This route enabled the encapsulation of organic material, difficult with other routes, under mild temperature and pressure conditions.

Once the microcapsules were obtained, the thesis analysed the effect of the addition of these to the cement matrix, to verify the viability of the technique. With this in mind, Ms Kaltzakorta used a number of techniques with which the features of the new cement material could be studied, techniques such as X-ray tomography, scanning electron microscopy, mechanical testing and differential scanning calorimetry.

In conclusion, the thesis shows the viability of the development of a new generation of cements capable of the self-repair of cracks as well as storing latent heat energy, based on the application of silica microcapsules with various organic materials. In fact, the research for developing the new cement with the capacity for self-sealing of cracks has given rise to a patent. Moreover, according to Ms Kaltzakorta, the proposal presented in this thesis is a commitment to sustainability. On the one hand, getting the cement material to self-repair increases the useful life of the structures. On the other, using a material capable of regulating the temperature within the buildings will enhance their energy efficiency.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Basque Research.